This invention relates generally to motor vehicle battery charger systems and in particular to motor vehicle battery charger systems that are mounted on and carried with the vehicle.
It has been the practice in the past to recharge motor vehicle batteries outside the vehicle. In most cases, the battery chargers of the prior art were bulky and required vacuum tubes in order to provide the high direct current requirements for charging low voltage, 6 and 12 volt, batteries used in a motor vehicle electrical system. To carry such apparatus on a motor vehicle would be impractical because of the space requirements needed to house the charger. However, with the advent of high current density solid state devices, the size of moderately high current density battery charges has become smaller.
For most automotive needs, the automobile generator provides sufficient charging capacity for the average vehicle, however, for vehicles in which added electrical accessories have been installed, such as and for emergency vehicles such as CB radios, radio telephones, spot lights, roof mounted emergency signals, etc., fire engines and the like, which can be inactive for long periods of time, batteries must be fully charged at all times for maximum service.
In addition, battery charges for such vehicles must be fail-safe and require no additional activities on the part of the vehicle user to manually perform a separate act to disconnect the power source from the charger when the vehicle is started and set in motion, or to remember to disconnect the charger from the battery.
For vehicles with dual battery systems, precautions must also be taken to prevent the flow of current between batteries when the battery charger is not energized but permanently connected to the vehicle battery system.
The many battery charger systems of the prior art seem to have concentrated their effort on circuits for charging dual battery systems but provide no fail-safe circuitry when the charger loses its power while remaining connected to the battery.